The present invention relates to a piezoelectric/electrostrictive device that is provided with a movable section to be operated on the basis of a displacement action of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device that is capable of detecting displacement of a movable section by the aid of a piezoelectric/electrostrictive element, and a method of producing the same. In particular, the invention relates to a piezoelectric/electrostrictive device that is excellent in strength, shock resistance, and moisture resistance and that makes it possible to efficiently operate a movable section to a great extent, and a method of producing the same.
Recently, a displacement element, which makes it possible to adjust the optical path length and the position in an order of submicron, is demanded, for example, in the fields of optics, magnetic recording, and precision machining. Development is advanced for the displacement element based on the use of the displacement brought about by the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in FIG. 23, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixing section 204, a movable section 206, and a beam section 208 for supporting the fixing and movable sections, which are formed integrally with a hole 202 provided through a plate-shaped member 200 composed of a piezoelectric/electrostrictive material and with an electrode layer 210 provided on the beam section 208 (see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer 210, the beam section 208 makes expansion and contraction in a direction along a line obtained by connecting the fixing section 204 and the movable section 206 in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section 206 can perform circular arc-shaped displacement or rotational displacement in the plane of the plate-shaped member 200.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation to an actuator based on the use of a bimorph. In this Substitute specification paragraphs technique, the electrodes of the bimorph actuator are provided in a divided manner. The actuator is driven due to the selection of the divided electrodes, and thus highly accurate positioning is performed at a high speed. JP ""640 discloses a structure (especially in FIG. 4) in which, for example, two opposed bimorphs are used.
However, the piezoelectric actuator described above involves a problem that the amount of operation of the movable section 206 is small, because the displacement in the direction of extension and contraction of the piezoelectric/electrostrictive material (i.e., in the in-plane direction of the plate-shaped member 200) is transmitted to the movable section 206 as it is.
Since all the parts of the piezoelectric actuator are made of piezoelectric/electrostrictive materials, which are fragile materials having a relatively heavy weight, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Furthermore, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation). In particular, the piezoelectric actuator has a weakness for torsion.
Then, a method may be adopted which increases the strength and the resonant frequency by thickening a beam portion, for example, in order to improve stiffness. However, displacement and a response speed are significantly deteriorated due to the improvement of stiffness.
The present invention has been made taking the foregoing problems into consideration, and an object thereof is to provide a piezoelectric/electrostrictive device and a method for manufacturing the same. According to the piezoelectric/electrostrictive device of the present invention, it is possible to obtain a displacement element which is scarcely affected by harmful vibration during operation and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance, making it possible to allow a reliable displacement operation in a two-dimensional plane and improve a resonance frequency and the displacement operation. Further, according to the piezoelectric/electrostrictive device of the present invention, it is possible to obtain a sensor element which accurately detects vibration of a movable section.
According to the present invention, a piezoelectric/electrostrictive device has a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section. The piezoelectric/electrostrictive device includes one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections. A hole is formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixing section.
The piezoelectric/electrostrictive device also includes at least one beam section provided from the inner wall of the movable section to the inner wall of the fixing section.
Since the beam section is provided from the inner wall of the movable section to the inner wall of the fixing section, the rigidity and the torsional strength of the piezoelectric/electrostrictive device is improved without increasing the thickness of the thin plate sections. Further, it is possible to realize a high resonance frequency. Furthermore, since the thickness of the thin plate section is not necessarily increased, the material characteristics of the piezoelectric/electrostrictive device formed with the thin plate sections are not deteriorated. Accordingly, it is possible to prevent a decrease in displacement.
Furthermore, since the piezoelectric/electrostrictive device has a displacement mode in which the movable section is moved in substantially parallel, the decrease in displacement due to the provision of the beam section is small, and the strength is advantageously increased. In particular, a structure having a resistance against lateral stress and torsional stress on the thin plate section is obtained.
As described above, in the piezoelectric/electrostrictive device of the invention, the control of the rigidity can be finely adjusted by changing the number, width, and thickness of the beam section without affecting the piezoelectric/electrostrictive element. In particular, torsion is suppressed owing to the provision of the beam section, and the displacement mode substantially in a two-dimensional plane can be conducted for the displacement operation.
The movable section, the fixing section, and the thin plate sections can be made of ceramics or metal. That is, each of the components may be made of a ceramic material, or each of the components may be made of a metal material. Alternatively, each of the components may be constructed to have a hybrid structure obtained by combining those produced from materials of ceramics and metal.
Furthermore, when the plane of the thin plate section where the piezoelectric/electrostrictive element is formed is designated as a side surface of the thin plate section, and the length in the direction of the minor side of the side surface of the thin plate section is designated as a width of the thin plate section, it is preferable from the standpoint of the contribution ratio of rigidity that the width of the beam section is ⅕ or more, and more preferably from ⅓ to {fraction (1/1)}, of the width of the thin plate section.
Furthermore, when the plane of the thin plate section where the piezoelectric/electrostrictive element is formed is designated as a side surface of the thin plate section, and the length in the direction of the major side of the side surface of the thin plate section is designated as a length Le of the thin plate section, it is preferable that the ratio (Le/Tb) of the length of the thin plate section to the total thickness of the beam section (Tb) is from 5 to 200.
The thin plate sections, the movable section, and the fixing section may comprise an integrated ceramic substrate formed by co-firing a ceramic green laminate, followed by cutting off unnecessary portions. Further, the piezoelectric/electrostrictive elements may be of a film form and integrated with the ceramic substrate by firing.
Moreover, the piezoelectric/electrostrictive elements may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on the piezoelectric/electrostrictive layer. The piezoelectric/electrostrictive element may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on both sides of the piezoelectric/electrostrictive layer, and one electrode of the pair of electrodes may be formed on at least the thin plate section. In this arrangement, the vibration caused by the piezoelectric/electrostrictive element can be efficiently transmitted via the thin plate section to the movable section or the fixing section. Thus, it is possible to improve the response performance. Further, it is preferable that the piezoelectric/electrostrictive elements are constructed by laminating a plurality of the piezoelectric/electrostrictive layers and the pairs of electrodes.
As described above, according to the present invention, it is possible to obtain a displacement element which is scarcely affected by harmful vibration during operation and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance, making it possible to allow a reliable displacement operation in a two-dimensional plane and improve a resonance frequency and the displacement operation. Further, it is possible to obtain a sensor element which accurately detects vibration of a movable section. According to the invention, the hole may be filled with a gel-like material.
According to the present invention, a method is provided for producing a piezoelectric/electrostrictive device having a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section. The piezoelectric/electrostrictive device includes one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections, and a hole is formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixing section.
The method includes the step of cutting off a predetermined portion, after forming the piezoelectric/electrostrictive elements on at least the thin plate sections, to produce the piezoelectric/electrostrictive device having at least one beam section from the inner wall of the movable section to the inner wall of the fixing section.
The phrase xe2x80x9cafter forming the piezoelectric/electrostrictive elementsxe2x80x9d referred to herein indicates a state in which at least the piezoelectric/electrostrictive layer is formed on the thin plate section. As for the electrode to be formed after the formation of the piezoelectric/electrostrictive layer, the electrode may be formed after conducting cutoff for forming the movable section or the fixing section that have mutually opposing end surfaces.
Further, according to the present invention, a method is provided for producing a piezoelectric/electrostrictive device having a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section. The piezoelectric/electrostrictive device includes one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections, and a hole is formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixing section.
The method includes the steps of producing a ceramic laminate by firing a ceramic green laminate containing first ceramic green sheets and second ceramic green sheets for constituting the thin plate sections integrally, the first ceramic green sheets each having a window for forming at least the hole and one or more beam sections. The piezoelectric/electrostrictive elements are formed on a part of an outer surface of the ceramic laminate for constituting the thin plate sections.
A piezoelectric/electrostrictive device having at least one beam section from the inner wall of the movable section to the inner wall of the fixing section is then produced by cutting at least once the ceramic laminate having the piezoelectric/electrostrictive element.
According to the above production methods, it is possible to obtain a displacement element which is scarcely affected by harmful vibration during operation and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance, making it possible to allow a reliable displacement operation in a two-dimensional plane and improve a resonance frequency and the displacement operation. Further, it is possible to obtain a sensor element which accurately detects vibration of a movable section.
In the production methods, the exposure of the hole can be also performed in the cutting step by cutting the ceramic laminate. In this case, the movable section or the fixing section having opposing end surfaces, and the hole can be made simultaneously. However, the movable section or the fixing section and the hole can also be made separately.
Therefore, the piezoelectric/electrostrictive device according to the present invention can be utilized as the active device including, for example, vibrators, resonators, oscillators, and discriminators for the communication and the power generation, various transducers, various actuators, frequency region functional parts (filters), transformers, as well as the sensor element for various sensors including, for example, ultrasonic sensors, acceleration sensors, angular velocity sensors, shock sensors, and mass sensors. Especially, the piezoelectric/electrostrictive device according to the present invention can be preferably utilized for various actuators to be used as the mechanism for adjusting the displacement and positioning and for adjusting the angle of various precision parts of optical instruments and precision mechanical equipment.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the invention is shown by way of illustrative example.